Analog peak power management for multi-die operations

ABSTRACT

Methods of peak power management (PPM) for a storage system having multiple memory dies are disclosed. Each memory die includes a first PPM circuit and a second PPM circuit. First PPM circuits of the multiple memory dies are electrically connected to form a first PPM group. Similarly, second PPM circuits are electrically connected to form a second PPM group. Peak power operations can be managed by switching on a first pull-down driver of the first PPM circuit on a selected memory die when a first PPM enablement signal of the first PPM group is zero; waiting for a first delay period; switching on a second pull-down driver of the second PPM circuit on the selected memory die when a second PPM enablement signal of the second PPM group is zero. The first and second PPM enablement signals depend on the current flowing through each pull-down driver in the first and second PPM groups.

INCORPORATION BY REFERENCE

This application is a continuation of U.S. patent application Ser. No. 17/116,253, filed on Dec. 9, 2020 and titled “Analog Peak Power Management For Multi-Die Operations,” which claims priority to PCT/CN2020/128024 filed on Nov. 11, 2020, both of which are incorporated herein by reference in their entirety.

TECHNICAL FIELD

The present disclosure generally relates to the field of semiconductor technology, and more particularly, to circuit designs and methods for peak power management in a storage system.

BACKGROUND

In many servers and mobile devices, NAND storage system is widely used as the primary non-volatile storage device due to its high storage density and relatively low access latency. However, performance of a high density storage system, for example, a three-dimensional (3D) NAND storage system, is often restricted by the maximum amount of power (or peak current) that it can use. Currently, operations consuming high power (i.e., peak power operations) that are carried out by various memory dies of the NAND storage system, can be staggered by a system controller. Only a limited number of peak power operations can be performed simultaneously. This approach can also result in increased system loading with unnecessary over-management. Communications between different memory dies can be established to coordinate the peak power operations. Currently, coordination between two memory dies can be arranged and peak power operations can be staggered between these two memory dies. When memory dies are grouped into two dies per group, coordination between groups remains an issue. Other approaches can provide multiple memory dies in each group to coordinate peak power operations, but are also limited to one peak power operation in each group. Therefore, it is necessary to optimize the control circuits and peak power management scheme to coordinate multiple memory dies simultaneously to allow multiple peak power operations performed in a storage system. As such, the storage system's power or current budget can be fully utilized.

BRIEF SUMMARY

An object of the present disclosure is to provide effective peak power management for a memory storage system.

One aspect of the present disclosure provides a peak power management (PPM) system for a storage system with multiple memory dies. The PPM system includes two or more PPM groups, each of the two or more PPM groups having multiple PPM circuits. Each of the multiple PPM circuits includes a pull-up driver electrically connected to a power source and a pull-up resistor; a pull-down driver electrically connected to a pull-down resistor; and a PPM pin connected to the pull-up resistor and the pull-down resistor. The PPM pins in each of the two or more PPM groups are electrically connected with each other. Each of the two or more PPM groups is configured to manage m number of peak power operations based on an electric potential of the PPM pins, where m is a whole number.

In some embodiments, each memory die includes at least one PPM circuit.

In some embodiments, the electric potentials of the PPM pins in each of the two or more PPM groups is determined by pull-down currents flowing through the pull-down drivers in the multiple PPM circuits.

In some embodiments, each of the two or more PPM groups further includes a comparator with a first input terminal electrically connected to the PPM pins and a second input terminal electrically connected to a reference voltage. An output terminal of the comparator is connected to an inverter.

In some embodiments, each of the two or more PPM groups further includes a resistance/capacitance (RC) filter electrically connected to the PPM pins and the first input terminal of the comparator.

In some embodiments, the reference voltage is in a range between a first electric potential of the PPM pins and a second electric potential of the PPM pins, the first electric potential and the second electric potential of the PPM pins corresponding to m−1 and m number of peak power operations, respectively.

In some embodiments, the first electric potential of the PPM pins is

${\frac{R_{d}}{R_{d} + {\left( {m - 1} \right) \cdot R_{u}}}V_{dd}},$ and the second electric potential of the PPM pins is

${\frac{R_{d}}{R_{d} + {m \cdot R_{u}}}V_{dd}},$ wherein R_(u) is the resistance of the pull-up resistor; R_(d) is the resistance of the pull-down resistor; and V_(dd) is the power source voltage.

In some embodiments, the pull-up driver is a p-channel metal oxide semiconductor field effect transistor (MOSFET), and the pull-down driver is an n-channel metal oxide semiconductor field effect transistor (MOSFET).

In some embodiments, the PPM pins in each PPM group are electrically connected through die-to-die connections, each die-to-die connection comprising a metal interconnect.

In some embodiments, the PPM pins in each PPM group are electrically connected through flip-chip bonding, die-to-die bonding, or wire-bonding.

The present disclosure also provides a method of peak power management (PPM) for a storage system with multiple memory dies, wherein each of the multiple memory dies includes a first PPM circuit and a second PPM circuit. First PPM circuits of the multiple memory dies are electrically connected to form a first PPM group, and second PPM circuits of the multiple memory dies are electrically connected to form a second PPM group. The method includes the following steps: switching on a first pull-down driver of the first PPM circuit on a selected memory die when a first PPM enablement signal of the first PPM group is zero; waiting for a first delay period; switching on a second pull-down driver of the second PPM circuit on the selected memory die when a second PPM enablement signal of the second PPM group is zero; and performing a peak power operation on the selected memory die. The first and second PPM enablement signals depend on the current flowing through each of the pull-down drivers in the first and second PPM groups.

In some embodiments, after performing the peak power operation, the second pull-down driver of the second PPM circuit on the selected memory die is switched off.

In some embodiments, after switching off the second pull-down driver of the second PPM circuit, the first pull-down driver of the first PPM circuit is switched off.

In some embodiments, prior to switching off the first pull-down driver of the first PPM circuit, a second delay period is performed.

In some embodiments, the second delay period is a predetermined time period.

In some embodiments, the first delay period is a time period unique to the selected memory die among the multiple memory dies in the storage system.

In some embodiments, the method further includes polling and checking, repeatedly, the first PPM enablement signal and the second PPM enablement signal when the first PPM enablement signal and/or the first PPM enablement signal is not zero.

In some embodiments, the method further includes generating the first PPM enablement signal by comparing a reference voltage with a first electric potential of a first plurality of PPM pins of the first PPM circuits in the first PPM group, wherein the first PPM circuits are electrically connected through the first plurality of PPM pins; and generating the second PPM enablement signal by comparing the reference voltage with a second electric potential of a second plurality of PPM pins of the second PPM circuits in the second PPM group, wherein the second PPM circuits are electrically connected through the second plurality of PPM pins.

In some embodiments, the generating of the first PPM enablement signal further includes setting the first PPM enablement signal to 0 if the first electric potential of the first plurality of PPM pins is higher than the reference voltage; and the generating of the second PPM enablement signal further comprises setting the second PPM enablement signal to 0 if the second electric potential of the second plurality of PPM pins is higher than the reference voltage.

In some embodiments, the generating of the first PPM enablement signal further comprises setting the first PPM enablement signal to 1 f the first electric potential of the first plurality of PPM pins is less than the reference voltage; and the generating of the second PPM enablement signal further comprises setting the second PPM enablement signal to 1 f the second electric potential of the second plurality of PPM pins is less than the reference voltage.

In some embodiments, the method also includes selecting the reference voltage based on a maximum m number of peak power operations for the storage system.

In some embodiments, the method further includes regulating the first electric potential of the first plurality of PPM pins through the first pull-down driver; and regulating the second electric potential of the second plurality of PPM pins through the second pull-down driver.

Other aspects of the present disclosure can be understood by those skilled in the art in light of the description, the claims, and the drawings of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and form a part of the specification, illustrate embodiments of the present disclosure and, together with the description, further serve to explain the principles of the present disclosure and to enable a person skilled in the pertinent art to make and use the present disclosure.

FIG. 1A illustrates a storage system with one or more NAND flash memories, according to some embodiments of the present disclosure.

FIG. 1B illustrates a top-down view of a memory die, according to some embodiments of the present disclosure.

FIG. 2 illustrates a peak power management system of a storage system, according to some embodiments of the present disclosure.

FIG. 3 illustrates a peak power management circuit, according to some embodiments of the present disclosure.

FIG. 4 illustrates an equivalent circuit of a peak power management group, according to some embodiments of the present disclosure.

FIG. 5 illustrates a peak power management scheme, according to some embodiments of the present disclosure.

FIG. 6 illustrates a peak power check routine, according to some embodiments of the present disclosure.

The features and advantages of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings, in which like reference characters identify corresponding elements throughout. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements.

Embodiments of the present disclosure will be described with reference to the accompanying drawings.

DETAILED DESCRIPTION

Although specific configurations and arrangements are discussed, it should be understood that this is done for illustrative purposes only. A person skilled in the pertinent art will recognize that other configurations and arrangements can be used without departing from the spirit and scope of the present disclosure. It will be apparent to a person skilled in the pertinent art that the present disclosure can also be employed in a variety of other applications.

It is noted that references in the specification to “one embodiment,” “an embodiment,” “an example embodiment,” “some embodiments,” etc., indicate that the embodiment described can include a particular feature, structure, or characteristic, but every embodiment can not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases do not necessarily refer to the same embodiment. Further, when a particular feature, structure or characteristic is described in connection with an embodiment, it would be within the knowledge of a person skilled in the pertinent art to affect such feature, structure or characteristic in connection with other embodiments whether or not explicitly described.

In general, terminology can be understood at least in part from usage in context. For example, the term “one or more” as used herein, depending at least in part upon context, can be used to describe any feature, structure, or characteristic in a singular sense or can be used to describe combinations of features, structures or characteristics in a plural sense. Similarly, terms, such as “a,” “an,” or “the,” again, can be understood to convey a singular usage or to convey a plural usage, depending at least in part upon context. In addition, the term “based on” can be understood as not necessarily intended to convey an exclusive set of factors and may, instead, allow for existence of additional factors not necessarily expressly described, again, depending at least in part on context.

As used herein, the term “nominal/nominally” refers to a desired, or target, value of a characteristic or parameter for a component or a process step, set during the design phase of a product or a process, together with a range of values above and/or below the desired value. The range of values can be due to slight variations in manufacturing processes or tolerances. As used herein, the term “about” indicates the value of a given quantity that can vary based on a particular technology node associated with the subject semiconductor device. Based on the particular technology node, the term “about” can indicate a value of a given quantity that varies within, for example, 10-30% of the value (e.g., ±10%, ±20%, or ±30% of the value).

FIG. 1A illustrates a storage system 10, according to some embodiments of the present disclosure. The storage system 10 (also referred to as a NAND storage system) can include a memory controller 20 and one or more NAND flash memories 100-1, 100-2, 100-3, . . . , 100-n (collectively referred to as NAND flash memories 100). The storage system 10 can communicate with a host computer 15 through the memory controller 20, where the memory controller 20 can be connected to the one or more NAND flash memories 100-1, 100-2, 100-3, . . . , 100-n, via one or more memory channels 30 (e.g., 30-1, 30-2, 30-3, . . . , 30-n). In some embodiments, each NAND flash memory 100 can be managed by the memory controller 20 via a memory channel 30.

The host computer 15 sends data to be stored at the storage system 10 or retrieves data by reading the storage system 10. The memory controller 20 can handle I/O requests received from the host computer 15, ensure data integrity and efficient storage, and manage the NAND flash memory 100. The memory channels 30 can provide data and control communication between the memory controller 20 and each NAND flash memory 100 via a data bus. The memory controller 20 can select one of the NAND flash memory 100 according to a chip enable signal.

FIG. 1B illustrates a top-down view of a NAND flash memory 100, according to some embodiments of the present disclosure. The NAND flash memory 100 can be a memory die (or a die) or any portion of a memory die. In some embodiments, each NAND flash memory 100 can include one or more memory planes 101, each of which can include a plurality of memory blocks 103. Identical and concurrent operations can take place at each memory plane 101. The memory block 103, which can be megabytes (MB) in size, is the smallest size to carry out erase operations. Shown in FIG. 1B, the exemplary NAND flash memory 100 includes four memory planes 101 and each memory plane 101 includes six memory blocks 103. Each memory block 103 can include a plurality of memory cells, where each memory cell can be addressed through interconnections such as bit lines and word lines. The bit lines and word lines can be laid out perpendicularly (e.g., in rows and columns, respectively), forming an array of metal lines. The direction of bit lines and word lines are labeled as “BL” and “WL” in FIG. 1B. In this disclosure, the memory block 103 is also referred to as the “memory array” or “array.” The memory array is the core area on a memory die, performing storage functions.

The NAND flash memory 100 also includes a periphery region 105, an area surrounding memory planes 101. The periphery region 105 contains peripheral circuits that include many digital, analog, and/or mixed-signal circuits to support functions of the memory array, for example, page buffers 50, row decoders 40, column decoders 60, control circuits 70 and sense amplifiers 80. Control circuits 70 include active and/or passive semiconductor devices, such as transistors, diodes, capacitors, resistors, etc., as would be apparent to a person of ordinary skill in the art.

It is noted that the layout of the electronic components in the storage system 10 and the NAND flash memory 100 in FIGS. 1A and 1B are shown as examples. The storage system 10 and the NAND flash memory 100 can have other layout and can include additional components. For example, the NAND flash memory 100 can also have high-voltage charge pumps, I/O circuits, etc. The storage system 10 can also include firmware, data scrambler, etc.

FIG. 2 illustrates a peak power management system 200, according to some embodiments of the present disclosure. The peak power management (PPM) system 200 can be implemented in the storage system 10 (in FIG. 1A), having a plurality of memory dies 100-1, 100-2, 100-3, . . . , 100-n. Each memory die can be similar to the NAND flash memory 100 discussed previously in reference with FIG. 1B. In some embodiments, each NAND flash memory 100 can include at least one peak power management (PPM) circuit. In the example shown in FIG. 2 , each NAND flash memory 100 includes a first PPM (PPM1) circuit 202 and a second PPM (PPM2) circuit 206. Each PPM1 circuit and each PPM2 circuit can include a PPM contact pad (also referred to as PPM pin). For example, each PPM1 circuit 202 includes a PPM1 contact pad 204 (also referred to as PPM1 pin), and each PPM2 circuit 206 includes a PPM2 contact pad 208 (also referred to as PPM2 pin). The PPM1 circuits 202-1, 202-2, 202-3, . . . , 202-n on different NAND flash memories 100-1, 100-2, 100-3, . . . , 100-n can communicate with each other through the PPM1 pins 204-1, 204-2, 204-3, . . . , 204-n. The PPM2 circuits 206-1, 206-2, 206-3, . . . , 206-n on different NAND flash memories 100-1, 100-2, 100-3, . . . , 100-n can communicate with each other through the PPM2 pins 208-1, 208-2, 208-3, . . . , 208-n. In some embodiments, the PPM pins between different NAND flash memories 100 can be electrically connected with each other through a plurality of die-to-die connections. For example, the PPM1 pins 204 between different NAND flash memories 100 can be electrically connected with each other through first die-to-die connections 205, and are thereby also referred to as a first PPM group 210 (or PPM1 group). Likewise, the PPM2 pins 208 between different NAND flash memories 100 can be electrically connected with each other through second die-to-die connections 209, and are thereby also referred to as a second PPM group 211 (or PPM2 group). In some embodiments, the first and second die-to-die connections 205 and 209 can be a metal wire formed through wire-bonding. In some embodiments, the first and second die-to-die connections 205 and 209 can be metal wires or any suitable metal or conductive material formed through flip-chip bonding or any suitable die-to-die bonding. In some embodiments, the first and second die-to-die connections 205 and 209 can be formed by through-silicon VIAs (e.g, through-array structures).

By using the die-to-die connections described above, communications between different memory dies (i.e., NAND flash memories 100-1, 100-2, 100-3, . . . , 100-n) can be established in the storage system. As such, the storage system 10 can send operation commands to any number of memory dies at any time while the PPM1 circuits 202 and the PPM2 circuits 206 can control the system's power consumption by selecting one or more memory dies.

FIG. 3 illustrates an exemplary PPM circuit 300 on the NAND flash memory 100, according to some embodiments of the present disclosure, where each of the PPM1 circuits 202 and each of the PPM2 circuits 206 shown in FIG. 2 can be similar to the PPM circuit 300. The PPM circuit 300 can include a pull-up driver 314, where one terminal of the pull-up driver 314 is connected to a power source 312 with a voltage V_(dd). In some embodiments, the pull-up driver 314 can be a metal-oxide-semiconductor-field-effect-transistor (MOSFET). In some embodiments, the pull-up driver 314 can be a p-channel MOSFET (i.e., pFET), where a source terminal of the pFET 314 can be connected to the power source 312 and a drain terminal of the pFET 314 can be connected to a pull-up resistor 318 with a resistance R_(u).

In some embodiments, the PPM circuit 300 also includes a pull-down driver 336. In some embodiments, the pull-down driver 336 can be a MOSFET. In some embodiments, the pull-down driver 336 can be an n-channel MOSFET (i.e., nFET). A source terminal of the nFET 336 can be grounded, and a drain terminal of the nFET 336 can be connected to a pull-down resistor 320 with a resistance R_(d).

In some embodiments, the pull-up resistor 318 and the pull-down resistor 320 are electrically connected in series at a node 322, where the PPM contact pad (e.g., the PPM1 pin 204 or the PPM2 pin 208 in FIG. 2 ) can be electrically connected to the node 322. As described previously, all the PPM contact pads (e.g., the PPM1 pins 204) in one PPM group (e.g., the PPM1 group 210) can be electrically connected through the die-to-die connections (e.g., the first die-to-die connection 205). Thus, all the PPM contact pads of the same PPM group can be held to an electrical potential V_(ppm) at the node 322.

In some embodiments, the PPM circuit 300 can also include a comparator 328, with a first input terminal 324 at a reference voltage V_(ref) and a second input terminal 326 connected to the node 322. The comparator 328 can be an operational amplifier used for comparing an input voltage V_(in) at the second input terminal 326 with the reference voltage V_(ref) at the first input terminal 324, where an output voltage V_(out) at an output terminal 330 can indicate whether the input voltage V_(in) is above or below the reference voltage V_(ref). For example, the output voltage V_(out) can be a positive voltage when the input voltage V_(in) is larger than the reference voltage V_(ref). On the other hand, the output voltage V_(out) can be a negative voltage when the input voltage V_(in) is smaller than the reference voltage V_(ref).

In some embodiments, the output circuit of the PPM circuit 300 can further include an inverter 332 with an input terminal connected to the output terminal 330 of the comparator 328. The inverter 332 can invert an input signal. For example, when the output voltage V_(out) of the comparator 328 is a positive voltage, a PPM enablement signal enPPM generated by the inverter 332 at an output terminal 334 can be zero, i.e., the PPM enablement signal enPPM=0. On the other hand, when the output voltage V_(out) of the comparator 328 is a negative voltage, the PPM enablement signal enPPM=1. In the other words, when the electrical potential V_(ppm) at the node 322 is larger than the reference voltage V_(ref) (i.e., V_(ppm)>V_(ref)), the PPM enablement signal enPPM=0. When the electrical potential V_(ppm) at the node 322 is smaller than the reference voltage V_(ref) (i.e., V_(ppm)<V_(ref)), the PPM enablement signal enPPM=1.

In some embodiments, the output circuit can include an optional resistance/capacitance (RC) filter 344 connected between the node 322 and the second input terminal 326 of the comparator 328. The RC filter 344 can be used to filter out unwanted signals within a certain frequency range.

As discussed previously, all the PPM pins of the same PPM group are electrically connected, i.e., all the PPM pins of the same PPM group have the same electrical potential V_(ppm). In some embodiments, each PPM group may have one comparator 328 electrically connected at the node 322. And the PPM enablement signal enPPM indicates the electrical potential V_(ppm) for the PPM group. In the example shown in FIG. 2 , the PPM enablement signals for the PPM1 group 210 and the PPM2 group 211 can thereby be presented by the PPM enablement signal enPPM1 and the PPM enablement signal enPPM2, respectively.

It is noted that the resistance R_(u) and R_(d), the characteristic of the pFET 314 and the nFET 336, the electrical potential V_(ppm) at node 322 are not necessary to be the same between the PPM1 circuit 202 and the PPM2 circuit 206 shown in FIG. 2 . The symbols used for the exemplary PPM circuit 300 are only for illustration purpose and for simplicity to demonstrate the functionality of the PPM circuits.

In some embodiments, the pull-down driver 336 can be replaced by any suitable device that can be implemented as a current source with a pre-determined current level.

During operation, a first control signal 340 can be sent to a gate terminal 316 of the pFET 314 to switch the pFET 314 on or off. For example, if the first control signal 340 has a voltage less than a threshold voltage of the pFET 314, the pFET 314 can be switched on, and a conductive path can be formed from the power source 312 to the pull-up resistor 318. The current flowing through the pull-up driver 314 and the pull-up resistor 318 is also referred to as the pull-up current I_(pull_up). If the first control signal 340 has a voltage higher than the threshold voltage of the pFET 314, the pFET 314 can be switched off.

When a second control signal 342 is sent to a gate terminal 338 of the nFET 336, the nFET 336 can be switched on or off. For example, if the second control signal 342 has a voltage higher than a threshold voltage of the nFET 336, the nFET 336 can be switched on, and a conductive path can be formed from the pull-down resistor 320 to the ground. If the second control signal 342 has a voltage less than the threshold voltage of the nFET 336, the nFET 336 can be switched off.

In some embodiments, the pull-down driver 336 can be operated as a current controller. In this example, when the pull-down driver 336 is switched on, the magnitude of the current flowing through the pull-down resistor 320 (also referred to as pull-down current I_(pull_dn)) depends on the second control signal 342. When the pull-down driver 336 is an nFET, as shown in FIG. 3 , the pull-down current I_(pull_dn) can be determined by the voltage level of the second control signal 342 and the trans-conductance of the nFET 336. According to some embodiments of the present disclosure, a peak current I_(cc) of a memory die (e.g., the NAND flash memory 100-1) can correspond to the voltage level of the second control signal 342, and thereby correspond to the pull-down current I_(pull_dn). Therefore, the pull-down current I_(pull_dn) can function as a current mirror of the peak current I_(cc) of the memory die.

In some embodiments, the pull-down current I_(pull_dn) can be proportional to the peak current I_(cc). The pull-down current I_(pull_dn) an can be scaled down from the peak current I_(cc), a high current level needed by the memory die to perform a peak power operation. For example, if the memory die needs 200 mA of current to perform a peak power operation, the pull-down current I_(pull_dn) can be 20 μA. Therefore, the peak power operations can be regulated for each memory die through the pull-down current I_(pull_dn). Furthermore, through the die-to-die connections at the PPM contact pads, peak power operations throughout the entire storage system can be coordinated between different memory dies.

During operation, according to some embodiments of the present disclosure, only one pull-up driver 314 is switched on (i.e., enabled) within each PPM group (e.g., within the PPM1 group 210 or the PPM2 group 211 in FIG. 2 ) and the other pull-up drivers 314 in the same PPM group are switched off. As such, current only flows from the power source 312 through one pull-up resistor 318 in each PPM group. During operation, the pull-down driver 336 can be switched on or off depending on the status of the memory die, and can be independently controlled according to the PPM management scheme discussed below. For example, the NAND flash memory 100-1 (in FIG. 2 ) can perform a peak power operation using the peak current I_(cc) when the pull-down driver 336 of the PPM2 circuit 206-1 is switched on, where a conductive path can be formed from the pull-down resistor 320 through the pull-down driver 336 to the ground. The NAND flash memories 100-1 is prohibited from performing any peak power operation when the pull-down driver 336 of the PPM2 circuit 208-1 is switched off, where no current can flow through the pull-down driver 336 on the NAND flash memory 100-1.

The electric potential V_(ppm) of the node 322 (or the PPM pins) depends on the number of pull-down drivers 336 that are switched on in each PPM group. Because a peak power operation can be performed on a memory die when the pull-down driver 336 is switched on, by monitoring the electric potential V_(ppm), the number of peak power operations performed in a storage system having multiple memory dies can thereby be regulated.

FIG. 4 shows an equivalent circuit of a PPM group, according to some embodiments of the present disclosure. The PPM group can be the PPM1 group 210 or the PPM2 group 211 in a storage system in FIG. 2 . Since only the pull-up driver 316 and the pull-down drivers 336 that are switched on can form conductive paths, FIG. 4 omits those pull-up drivers 316 and pull-down drivers 336 that are switched off. As discussed previously, the node 322 is electrically connected to the PPM pin on the memory die, and all the PPM pins in the same PPM group are electrically connected between different memory dies. The node 322 can be held at the same electrical potential V_(ppm) in the entire PPM group between different memory dies, and is illustrated as one intersection point to the pull-up resistor 318 in FIG. 4 .

In some embodiments, only one pull-up driver 314 is switched on in one PPM group for peak power management. In some embodiments, the pull-down driver 336 is switched on in the PPM circuit corresponding to the memory die performing the peak power operation, i.e., using the peak current I_(cc).

In one example, there can be m number of peak power operations in the storage system 10, where m can be any whole number. For illustration purpose, it is assumed that one memory die can perform one peak power operation. Thus, there can be m number of memory dies (e.g., NAND flash memory 100-1, 100-2, . . . , 100-m in FIG. 2 ) performing peak power operations simultaneously in the storage system 10. The pull-down drivers 336 in the same PPM group are connected in parallel with each other. In this configuration, the pull-up current I_(pull_up) flowing through the pull-up driver 316 that is switched on, is the sum of the pull-down current I_(pull_dn) (e.g., I_(pull_dn-1), I_(pull_dn-2), . . . , I_(pull_dn-m)) flowing through each of the pull-down drivers 336 that are switched on. The equivalent circuit 400 functions as a voltage divider, and the electric potential V_(ppm) of the node 322 can be expressed as a function of m, the number of memory dies performing the peak power operation:

$\begin{matrix} {{V_{ppm}(m)} = {\frac{R_{d}}{R_{d} + {m \cdot R_{u}}}V_{dd}}} & (1) \end{matrix}$ Where R_(d) and R_(u) are the resistances of the pull-down resistor 320 and pull-up resistor 318, respectively, and the power source 312 provides the voltage V_(dd).

At the beginning of peak power management, any one of the pFETs 314 in the PPM group can be switched on. If there is no memory die performing peak power operation, none of the nFET 336 is switched on. The electric potential V_(ppm) of the node 322 is set to the voltage V_(dd) of the power source 312 through the conductive path established by the specific pFET 314 that is switched on. If V_(dd)=1.2V, then V_(ppm) (0)=1.2 V (at m=0).

When one of the memory dies, e.g., the NAND flash memory 100-1, is performing the peak power operation, the memory die consumes the peak current I_(cc-1). As discussed previously, the second control signal 342-1 can be generated to switch on the pull-down driver 336-1 to enable the peak power operation on the NAND flash memory 100-1. As such, the pull-down current I_(pull_dn-1) can flow through the pull-down driver 336-1 and the pull-down resistor 320-1. The electric potential V_(ppm) at the node 322 is changed to

${V_{ppm}(1)} = {\frac{R_{d}}{R_{d} + R_{u}}{{V_{dd}\left( {{{at}m} = 1} \right)}.}}$ Assuming the resistance R_(d) is twice as much as the resistance R_(u), the electric potential V_(ppm) (1)=⅔V_(dd)=0.8 V.

When another memory die, e.g., the NAND flash memory 100-2, is also performing the peak power operation, there are two memory dies (m=2) in the storage system 10 are now using the peak current I_(cc), i.e., the peak current I_(cc-1) on the NAND flash memory 100-1 and the peak current I_(cc-2) on the NAND flash memory 100-2. In some embodiments, the peak current I_(cc-1) of the NAND flash memory 100-1 and the peak current I_(cc-2) of the NAND flash memory 100-2 can be the same. In some embodiments, the peak current I_(cc-1) of the NAND flash memory 100-1 and the peak current I_(cc-2) of the NAND flash memory 100-2 can be the different. As discussed previously, the second control signal 342-2 can be generated to switch on the pull-down driver 336-2 to enable the peak power operation on the NAND flash memory 100-2. As such, the pull-down current I_(pull_du-2) can flow through the pull-down driver 336-2 and the pull-down resistor 320-2. The pull-down current I_(pull_dn-1) and the pull-down current I_(pull_dn-2) flow through the pull-down resistor 320-1 and the pull-down resistor 320-2, respectively, where the pull-down resistor 320-1 and the pull-down resistor 320-2 are connected in parallel. The electric potential V_(ppm) at the node 322 is then changed to

${V_{ppm}(2)} = {\frac{R_{d}}{R_{d} + {2 \cdot R_{u}}}{{V_{dd}\left( {{{at}m} = 2} \right)}.}}$ If assuming that the resistance R_(d) is twice as much as the resistance R_(u), the electric potential V_(ppm) (2)=½V_(dd)=0.6 V.

When a third memory die, e.g., the NAND flash memory 100-3, is also performing the peak power operation, i.e., three memory dies (m=3) in the storage system 10 are consuming the peak current I_(cc), the electric potential V_(ppm) at the node 322 is then changed to

${V_{ppm}(3)} = {\frac{R_{d}}{R_{d} + {3 \cdot R_{u}}}{{V_{dd}\left( {{{at}m} = 3} \right)}.}}$ If assuming that the resistance R_(d) is twice as much as the resistance R_(u), the electric potential V_(ppm) (3)=⅖V_(dd)=0.48 V.

Using the Equation (1), the electric potential V_(ppm) can be calculated if four memory dies (m=4) in the storage system 10 are using the peak current I_(cc), i.e. performing the peak power operations. The electric potential

${{{V_{ppm}(4)} = {\frac{R_{d}}{R_{d} + {4 \cdot R_{u}}}V_{dd}}};{or}}{{V_{ppm}(4)} = {{\frac{1}{3}V_{dd}} = {0.4V{\left( {{{{if}V_{dd}} = {1.2V}},{R_{d} = {2R_{u}}}} \right).}}}}$ The electric potentials V_(ppm) (m) are listed in FIG. 5 for various number of peak power operations (i.e., 0, 1, 2, 3, 4, . . . , m−1, m).

FIG. 5 illustrates an exemplary peak power management scheme, according to some embodiments of the present disclosure. In this example, the voltage V_(dd) of the power source 312 is assumed to be 1.2 V. The resistance R_(d) of the pull-down resistor 320 is assumed to be twice as much as the resistance R_(u) of the pull-up resistor 318. It is noted that the assumptions of the voltage V_(dd) and the resistances R_(u) and R_(d) are chosen to provide an illustration of the principles of the peak power management scheme in the present disclosure. A person of ordinary skill in the art can utilize the principle of the peak power management scheme described here with various modifications as suitable for the practical applications. All such modifications and variations are within the scope of the present disclosure.

As discussed above, the electric potential V_(ppm) of a PPM group depends on the number of peak power operations. According to Equation (1) and FIG. 5 , the electric potential V_(ppm) decreases when the number of the peak power operations increases. Therefore, the reference voltage V_(ref) for the comparator 328 (in FIG. 3 ) can be chosen such that the PPM enablement signal enPPM can be set at enPPM=0 when the electric potential V_(ppm) is higher than the reference voltage V_(ref), i.e., when the number of memory dies performing peak power operations is less than a predetermined number. And the PPM enablement signal enPPM can be set at enPPM=1 when the electric potential V_(ppm) is lower than the reference voltage V_(ref), i.e., when the number of memory dies performing peak power operations has reached (equal or greater than) the predetermined number. In the other words, the reference voltage V_(ref) can be programmed to correspond to the maximum number of peak power operations allowed in a storage system. Accordingly, when the PPM enablement signal enPPM=0, the storage system can still provide additional peak current I_(cc) to at least one of the memory dies, i.e., having enough power (or current) to provide at least one additional memory die to perform peak power operation. On the contrary, when the PPM enablement signal enPPM=1, the maximum number of peak power operations have been reached for the storage system. The storage system has reached its power (or current) limit and cannot provide additional peak current I_(cc) to any of the memory dies to perform any additional peak power operation.

For a storage system where each memory die includes more than one PPM group, one reference voltage V_(ref) can be chosen for each PPM group to output a PPM enablement signal enPPM for controlling a maximum number of peak power operations. In the example of the storage system in FIG. 2 , the PPM1 group can have a reference voltage V_(ref-1) programed to correspond to a number m₁— the maximum number of peak power operations allowed in the PPM1 group. Similarly, the PPM2 group can have a reference voltage V_(ref-2) programed to correspond to a number m₂— the maximum number of peak power operations allowed in the PPM2 group.

For illustration purpose below, it is assumed that the maximum number of peak power operations in a storage system (or in each memory group) is the number m, and each memory die can perform a peak power operation at a time. It is noted that these assumptions are chosen for simplicity and should not limit the scope of this disclosure. For example, each memory die can perform two or more peak power operations simultaneously.

According to Equation (1), if there are m−1 number of peak power operations, the electric potential V_(ppm) can be expressed as:

$\begin{matrix} {{V_{ppm}\left( {m - 1} \right)} = {\frac{R_{d}}{R_{d} + {\left( {m - 1} \right) \cdot R_{u}}}V_{dd}}} & (2) \end{matrix}$ Thus, the reference voltage V_(ref) (m), corresponding to the maximum number m of peak power operations, can be set to a voltage in a range between the electric potential V_(ppm) (m) and the electric potential V_(ppm) (m−1):

$\begin{matrix} {{\frac{R_{d}}{R_{d} + {m \cdot R_{u}}}V_{dd}} < {V_{ref}(m)} < {\frac{R_{d}}{R_{d} + {\left( {m - 1} \right) \cdot R_{u}}}V_{dd}}} & (3) \end{matrix}$

In the example shown in FIG. 5 , if the maximum number of peak power operations allowed is 2, the reference voltage V_(ref) can be a voltage in a range between V_(ppm) (2)=0.6 V and V_(ppm) (1)=0.8 V, where V_(ref) (2)=0.7 V is chosen in FIG. 5 as an example. If the electric potential V_(ppm) is less than the reference voltage V_(ref)=0.7 V, the PPM enablement signal enPPM=0 is generated at the output terminal 334 (see FIG. 3 ), indicating that the number of peak power operations is 0 or 1, less than the maximum number of 2. The storage system can have at least one additional peak power operation performed by at least one of the memory dies. When there are two peak power operations performed simultaneously, i.e., two memory dies are consuming the peak current I_(cc), the electric potential V_(ppm)=0.6 V, lower than the reference voltage V_(ref)=0.7 V. The PPM enablement signal enPPM=1 s generated accordingly, indicating that the maximum number of peak power operations of 2 has been reached. The NAND storage system can then prohibit additional memory die to perform a peak power operation. As such, the PPM enablement signal enPPM can function as an indicator for the number of peak power operations performed in the storage system with multiple memory dies.

As discussed above, the PPM enablement signal enPPM for each PPM group can be generated by comparing the reference voltage V_(ref) with the electric potential V_(ppm) of the PPM pins (or at the node 322) that are electrically connected between the memory dies. The PPM enablement signal enPPM is set to 0 if the electric potential V_(ppm) of the PPM pins is higher than the reference voltage V_(ref). The PPM enablement signal enPPM is set to 1 f the electric potential V_(ppm) of the PPM pins is less than the reference voltage V_(ref). Because the electric potential V_(ppm) depends on the pull-down current I_(pull-dn), flowing through each of the pull-down drivers in the PPM group, and the pull-down driver is switched on when peak power operation is performed on the corresponding memory die, thus the reference voltage can be selected based on a maximum m number of peak power operations for the storage system.

FIG. 6 illustrates a peak power check routine 600 associated with the peak power management system 200 in FIG. 2 and the PPM circuit 300 in FIG. 3 , according to some embodiments of the present disclosure. The PPM schemes shown in FIGS. 4 and 5 are used to determine the reference voltage V_(ref) and generate the PPM enablement signal enPPM to indicate the maximum number of peak power operations allowed in a storage system. It should be understood that the peak power check (PPC) routine 600 are not exhaustive and that other operation steps can be performed as well before, after, or between any of the illustrated operation steps. In some embodiments, some operation steps of the PPC routine 600 can be omitted or other operation steps can be included, which are not described here for simplicity. In some embodiments, operation steps of the PPC routine 600 can be performed in a different order and/or vary.

The PPC routine 600 provides an exemplary method of managing peak power usage for a storage system with one or more memory dies, where each memory die includes at least one PPM circuit. The example below is shown for a storage system, e.g., the storage system in FIG. 2 , where each memory die includes two PPM circuits, the PPM1 circuit 202 and the PPM2 circuit 206. Accordingly, the storage system includes two PPM groups, the PPM1 group 210 and the PPM2 group 211 for checking and regulating peak power operations performed by the memory dies. However, the method can be extended to a storage system where each memory die includes one or more PPM circuits.

The PPC routine 600 can be implemented before a memory die starts to perform a peak power operation such that the total power (or current) consumed by a storage system can be regulated and controlled to below a predetermined value.

The PPC routine 600 starts at operation step S605, when a storage system (e.g., the NAND storage system 10 in FIG. 1 ) determines that a memory die (e.g., the NAND flash memory 100-1 in FIG. 2 ) is ready to start a peak power operation. At the operation step S605, the PPM circuits (e.g., the first PPM circuit 202-1 and the second PPM circuit 206-1) on the NAND flash memory 100-1 are at a reset state. At the reset state, the pull-down drivers 336 in the PPM1 circuit 202-1 and the PPM2 circuit 206-1 are switched off. At the operation step S605, one of the pull-up drivers 314 in the PPM1 group 210 can be switched on if none of the pull-up drivers 314 in the PPM1 group 210 has been switched on. Similarly, one of the pull-up drivers 314 in the PPM2 group 211 can be switched on if none of the pull-up drivers 314 in the PPM2 group 211 has been switched on.

At operation step S610, the PPC routine 600 enters a first check point, where the PPM enablement signal enPPM1 of the PPM1 group is verified. If the PPM enablement signal enPPM1 is not zero (e.g., enPPM1=1), the PPC routine 600 pauses at operation step S615 and the PPM enablement signal enPPM1 is polled and verified again at operation step S610. As discussed previously, when the PPM enablement signal enPPM1=1, a maximum number of peak power operations have been reached, and the storage system cannot support any additional peak power operations or provide any additional operation using the peak current I_(cc). Thus, when the PPM enablement signal enPPM1=1, the NAND flash memory 100-1 is prohibited to perform a peak power operation and must wait until the status of the enPPM1 is changed.

When the PPM enablement signal enPPM1 is zero, it is indicated that the storage system can support at least one additional peak power operation. The PPC routine 600 can then perform operation step S620.

At operation step S620, the pull-down driver 336-1 of the PPM1 circuit 202-1 on the NAND flash memory 100-1 can be switched on. If the resulting pull-down current I_(pull_dn-1) flowing through the pull-down driver 336-1 of the PPM1 circuit 202-1 can reduce the electric potential V_(ppm) of the PPM1 group to below the reference voltage V_(ref), the PPM enablement signal enPPM1 is set to 1 (i.e., enPPM1=1). As a result, no more other memory dies requesting peak power operation and running the PPC routine 600 can pass the first check point at the operation step S610 after the PPM enablement signal enPPM1 is set to 1. If the resulting pull-down current I_(pull_dn-1) flowing through the pull-down driver 336-1 of the PPM1 circuit 202-1 does not lower the electric potential V_(ppm) of the PPM1 group to a value less than the reference voltage V_(ref), the PPM enablement signal enPPM1 remains as zero (i.e., enPPM1=0). Other memory dies requesting peak power operation and running the PPC routine 600 can still pass the first check point at the operation step S610 until the PPM enablement signal enPPM1 is set to 1. As such one or more memory dies can run the PPC routine 600 simultaneously, and the peak power operations can be performed and coordinated more efficiently.

Next, at operation step S625, the PPC routine 600 is paused for a waiting period of a first delay period t_(dl_1), wherein the first delay period t_(dl_l) is different for each memory die. In the other words, the NAND flash memory 100-1 is assigned with the first delay period t_(dl_1) having a value different from any other NAND flash memories 100-2, 100-3, . . . 100-n in the same storage system. As such, when more than one memory die runs the PPC routine 600 simultaneously, each memory die waits for a different time period at the operation step S625. As discussed previously, the PPM pins of the same PPM group are electrically connected with each other and thus the memory dies in the same PPM group are controlled by the same electric potential V_(ppm). When the PPM enablement signal enPPM1 is zero (i.e., enPPM1=0) at operation step S610, one or more memory dies of the same storage system that is running the PPC routine 600 can enable (or switch on) the pull-down driver 336 at the same time. By imposing a unique time delay for each memory die, memory dies can enter the subsequent operation step S630 one at a time. The memory dies completing the operation step S620 at the same time, can be desynchronized at the operation step S625. The operation step S625 ensures that only one additional peak power operation can be allowed at any given time.

When the NAND flash memory 100-1 finishes the waiting period of the first delay period t_(dl_1), a second check point at operation step S630 can be resumed.

At operation step S630, the PPM enablement signal enPPM2 of the PPM2 group 211 is verified. If the PPM enablement signal enPPM2 is not zero (e.g., when enPPM2=1), the PPC routine 600 pauses at operation step S635 and the PPM enablement signal enPPM2 is polled and verified again at operation step S640. As discussed previously, when the PPM enablement signal enPPM2=1, a maximum number of peak power operations have been reached, and the storage system cannot support any additional peak power operation. Thus, when the PPM enablement signal enPPM2=1, the NAND flash memory 100-1 is prohibited to perform a peak power operation and must wait until the status of the enPPM2 is changed.

In some embodiments, the PPM enablement signal enPPM1 of the PPM1 group is zero at operation step S610, but the PPM enablement signal enPPM2 of the PPM2 group is not zero at operation step S630. In this example, additional peak power operation is started between the time period of the operation step S610 and operation step S630 by another memory die (e.g., NAND flash memory 100-2) in the storage system. For example, the NAND flash memory 100-2 completes operation step S625 before the NAND flash memory 100-1. By implementing operation steps S635 and S640, the memory die that has passed the first check point at operation step S610 can wait for its turn to perform a peak power operation.

When the PPM enablement signal enPPM2 is zero (i.e., enPPM2=0) at operation step S640, operation step S625 can be performed again to implement the first delay period t_(dl_1). And operation step S630 is performed again to verify if the PPM enablement signal enPPM2=0.

When the PPM enablement signal enPPM2=0 at operation step S630, the PPC routine 600 starts operation step S645, where the pull-down driver 336 of the PPM2 circuit 206-1 is switched on for the NAND flash memory 100-1.

At operation step S650, the NAND flash memory 100-1 starts to perform the peak power operation with the peak current I_(cc). If the maximum number of peak power operations have been reached after the NAND flash memory 100-1 starts the peak power operation, the electric potential V_(ppm) of the PPM2 group can be less than the reference voltage V_(ref) and thereby the PPM enablement signal enPPM2 is set to 1 (i.e., enPPM2=1). If the maximum number of peak power operations have not been reached after the NAND flash memory 100-1 starts the peak power operation, the electric potential V_(ppm) of the PPM2 group is still higher than the reference voltage V_(ref). The PPM enablement signal enPPM2 remains as zero (i.e., enPPM2=0).

At operation step S655, after completing the peak power operation, the pull-down driver 336 of the PPM2 circuit 206-1 can be disabled (i.e., switched off) for the NAND flash memory 100-1. Accordingly, the PPM enablement signal enPPM2 for the PPM2 group can be reset to zero again.

At operation step S660, the PPC routine 600 performs a second delay period t_(dl_2), where the second delay period t_(dl_2) can be a predetermined time period, for example, 2 μs. The second delay period t_(dl_2) is chosen such that the memory dies, which have completed operation steps S610 and S620 and are waiting at the operation steps S635 and S640, can complete the peak power operation at operation step S650 before the PPC routine 600 allows other memory dies to pass through the first check point at the operation step S610. As such, memory dies that are delayed at the operation step S625 can be queued for peak power operations and complete operation steps S645-S655 one at a time, prior to any memory die that have not entered the first check point at operation step S610.

At operation step S665, the pull-down driver 336 of the PPM1 circuit 202-1 on the NAND flash memory 100-1 is disabled (i.e., switched off). Accordingly, the PPM enablement signal enPPM1 for the PPM1 group can be reset to zero again. Another batch of multiple memory dies can subsequently pass the first check point at operation step S610 and are queued for peak power operations.

Through an analog processing of the electric potential V_(ppm) of the PPM pins connected between multiple memory dies, analog peak power management can be implemented. The PPM enablement signal enPPM can be used to encode with information regarding the number of peak power operations performed in a storage system. Multiple peak power operations below a maximum number can be performed simultaneously in a storage system with multiple memory dies. By using the PPC routine with two PPM groups, multiple memory dies can be queued and staggered for peak power operations once the power/current budget is available for the storage system.

As an example, the above analog peak power management method can be applied to an asynchronous multi-plane independent (AMPI) read operation. In a NAND storage system, each storage system includes multiple memory dies and each memory die can have multiple memory planes. For example, the NAND flash memory 100 shown in FIG. 1B includes four memory planes 101. Read operations from different memory planes need to be staggered to avoid coincidence of peak current, and thereby are referred to as AMPI read. In some embodiments, an AMPI read can be defined as a peak power operation. Each memory plane's AMPI can be controlled by a PPM circuit, or more specifically can be controlled through the pull-down driver. The PPM circuits from a group of memory planes can be electrically connected through the PPM pins to form a PPM group, where the maximum number of peak power operations can be predetermined according to the peak power (or peak current) budget of the NAND storage system.

The present disclosure also provides a method of peak power management (PPM) for a storage system with multiple memory dies, wherein each of the multiple memory dies includes a first PPM circuit and a second PPM circuit. First PPM circuits of the multiple memory dies are electrically connected to form a first PPM group, and second PPM circuits of the multiple memory dies are electrically connected to form a second PPM group. The method includes the following steps: switching on a first pull-down driver of the first PPM circuit on a selected memory die when a first PPM enablement signal of the first PPM group is zero; waiting for a first delay period; switching on a second pull-down driver of the second PPM circuit on the selected memory die when a second PPM enablement signal of the second PPM group is zero; and performing a peak power operation on the selected memory die. The first and second PPM enablement signals depend on the current flowing through each of the pull-down drivers in the first and second PPM groups.

The foregoing description of the specific embodiments will so fully reveal the general nature of the present disclosure that others can, by applying knowledge within the skill of the art, readily modify and/or adapt, for various applications, such specific embodiments, without undue experimentation, and without departing from the general concept of the present disclosure. Therefore, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed embodiments, based on the disclosure and guidance presented herein. It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation, such that the terminology or phraseology of the present specification is to be interpreted by the skilled artisan in light of the disclosure and guidance.

Embodiments of the present disclosure have been described above with the aid of functional building blocks illustrating the implementation of specified functions and relationships thereof. The boundaries of these functional building blocks have been arbitrarily defined herein for the convenience of the description. Alternate boundaries can be defined so long as the specified functions and relationships thereof are appropriately performed.

The Summary and Abstract sections can set forth one or more but not all exemplary embodiments of the present disclosure as contemplated by the inventor(s), and thus, are not intended to limit the present disclosure and the appended claims in any way.

The breadth and scope of the present disclosure should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents. 

What is claimed is:
 1. A peak power management (PPM) system for a storage system with multiple memory dies, comprising: a PPM group comprising multiple PPM circuits, wherein: each of the multiple PPM circuits is provided in a memory die and comprises a PPM pad, wherein: PPM pads in the PPM group are electrically connected with each other; and the multiple PPM circuits are configured to change an electric potential of the PPM pads according to a number of peak power operations performed on the multiple memory dies.
 2. The PPM system of claim 1, wherein each of the multiple PPM circuits further comprises a pull-up driver electrically connected between a power source and the PPM pad.
 3. The PPM system of claim 2, wherein only one pull-up driver is enabled within each PPM group and other pull-up drivers in a same PPM group are disenabled.
 4. The PPM system of claim 2, wherein each of the multiple PPM circuits further comprises a pull-down driver electrically connected between a ground and the PPM pad.
 5. The PPM system of claim 4, wherein the pull-down driver is controlled by a control signal corresponding to a peak power operation performed on a corresponding memory die in which the pull-down driver is provided.
 6. The PPM system of claim 4, wherein each of the multiple PPM circuits further comprises a pull-up resistor and a pull-down resistor, wherein the pull-up resistor and the pull-down resistor are connected in series with the pull-up driver and the pull-down driver, respetively, and are both electrically connected with the PPM pad.
 7. The PPM system of claim 1, wherein the electric potential of the PPM pads in the PPM group is determined by pull-down currents flowing through pull-down drivers in the multiple PPM circuits.
 8. The PPM system of claim 1, wherein the electric potential of the PPM pads decreases when the number of peak power operations performed on the multiple memory dies increases.
 9. The PPM system of claim 1, wherein each of the multiple PPM circuits further comprises an output circuit configured to output a PPM enablement signal for determining whether to enable an additional peak power operation in the storage system.
 10. The PPM system of claim 9, wherein the output circuit comprises a comparator with a first input terminal electrically connected to the PPM pad and a second input terminal electrically connected to a reference voltage.
 11. The PPM system of claim 10, wherein the reference voltage corresponds to a maximum number of peak power operations allowed in the storage system.
 12. A method of peak power management (PPM) for a storage system with multiple memory dies, wherein the storage system comprises a PPM group corresponding to the multiple memory dies and each of the multiple memory dies comprises a PPM circuit with a PPM pad electrically connected to other PPM pads in the PPM group, the method comprising: changing an electric potential of PPM pads in the PPM group according to a number of peak power operations performed on the multiple memory dies; and generating, based on the electric potential of the PPM pads, a PPM enablement signal for managing the number of the peak power operations for the multiple memory dies.
 13. The method of claim 12, wherein each of the multiple memory dies comprises a first PPM circuit in a first PPM group and a second PPM circuit in a second PPM group, the method further comprising: receiving a first PPM enablement signal from the first PPM group to enable a peak power operation in the storage system; switching on a first current flowing through a corresponding first PPM circuit on a selected memory die in the storage system; waiting for a first delay period; receiving a second PPM enablement signal from the second PPM group to enable the peak power operation in the storage system; and performing the peak power operation on the selected memory die.
 14. The method of claim 13, further comprising: after receiving the second PPM enablement signal, switching on a second current flowing through a corresponding second PPM circuit on the selected memory die.
 15. The method of claim 13, wherein the waiting for the first delay period comprises waiting for a time period unique to the selected memory die among the multiple memory dies in the storage system.
 16. The method of claim 13, further comprising: generating the first PPM enablement signal by comparing a reference voltage with a first electric potential of first PPM pads of first PPM circuits in the first PPM group, wherein the first PPM pads of the first PPM circuits on different memory dies are electrically connected with each other; and generating the second PPM enablement signal by comparing the reference voltage with a second electric potential of second PPM pads of second PPM circuits in the second PPM group, wherein the second PPM pads of the second PPM circuits on different memory dies are electrically connected with each other.
 17. The method of claim 16, further comprising: selecting the reference voltage based on a maximum number of peak power operations for the storage system.
 18. The method of claim 16, further comprising: changing the first electric potential of the first PPM group by switching on first currents flowing through the first PPM circuits in the first PPM group; and changing the second electric potential of the second PPM group by switching on second currents flowing through the second PPM circuits in the second PPM group.
 19. A memory die of a storage system, comprising: a peak power management (PPM) circuit comprising a PPM pad, wherein: the PPM pad is electrically connected with a further PPM pad of a further PPM circuit on a further memory die; and the PPM circuit and the further PPM circuit are is configured to change an electric potential of the PPM pad according to a number of peak power operations performed in the storage system.
 20. The memory die of claim 19, wherein the PPM circuit further comprises: a pull-up driver electrically connected between a power source and the PPM pad; and a pull-down driver electrically connected between a ground and the PPM pad.
 21. The memory die of claim 20, wherein the pull-down driver is controlled by a control signal corresponding to a peak power operation performed on the memory die.
 22. The memory die of claim 20, wherein the PPM circuit further comprises a pull-up resistor and a pull-down resistor, wherein the pull-up resistor and the pull-down resistor are connected in series with the pull-up driver and the pull-down driver, respectively, and are both electrically connected with the PPM pad.
 23. The memory die of claim 20, wherein the electric potential of the PPM pad is determined by a pull-down current flowing through the pull-down driver.
 24. The memory die of claim 19, wherein the PPM circuit further comprises an output circuit configured to output a PPM enablement signal for determining whether to enable an additional peak power operation in the storage system.
 25. The memory die of claim 24, wherein the output circuit comprises a comparator with a first input terminal electrically connected to the PPM pad and a second input terminal electrically connected to a reference voltage, wherein the reference voltage corresponds to a maximum number of peak power operations allowed in the storage system. 